Basement Window Well

[WiSEiwish]

Hello,

I am designing a reinforced concrete basement window well. I have a couple of elementary questions regarding the design, so bear with me.

The bottom of the wall will be below the frost line. The well is rectangular in geometry with side walls extending to the building at right angles. My first question is how deep should the wall extend below grade from the inside of the well? My second question is what should the profile look like at the bottom of the wall? Should it look like a strip footing, or will a straight wall be adequate. The load is nothing more than a small (50psf) surcharge and the at rest soil pressure.

 

[jittles]

I believe you answered your first question yourself.

The bottom of the wall will be below the frost line.

The frost depth needs to be measured from the lowest grade level, i.e. the bottom of the inside of the well.

The bottom of the wall may very well not need a wider footing by design, but check your code minimum requirements and/or the geotech report.

 

[JAE]

Sometimes window wells are designed as free box retainers and not tied tight to the building, allowing frost heave relative to the building.

 

[SLTA]

I like JAE's suggestion. It also leaves less inclination for water intrusion later, when the well and the wall want to move separately from each other.

 

[WiSEiwish]

Can you explain what a "free box retainer" is? My understanding is that the well is not rigidly attached to the building and doesn't necessarily have to extend below the line of frost as referenced from the inside of the well. Since it is not rigidly attached to the building, the well may experience frost heave if the environment dictates, but, since it is not fastened to the building, it does not cause any structural damage. In addition, since there is no bottom to the well, any water can drain away.

I guess the question, then, is how far does the bottom of the well have to be embedded from the reference point of the inside of the well if extending it below the frost line is not a requirement?

 

[JAE]

Perhaps 12" to 18"

 

[jittles]

I would say it doesn't have to go below grade whatsoever, as long as you don't need it to by design.